A well known deficiency of global navigation satellite systems (GNSS), such the Global Positioning System (GPS), is that oscillator quartz crystals in these systems exhibit isolated temperature induced frequency jumps, typically on the order of 1-100 parts per billion (ppb). These so called “micro-jumps” have been found to be disruptive to the carrier and sometimes the code tracking loops used in precision GNSS equipment, and may, if severe, cause temporary loss of satellite tracking. Typically, temperature compensated quartz oscillators are prescreened over temperature for frequency jumps and rejected if jumps larger than some maximum limit is measured (e.g., 10 m/sec (33 ppb)). Here, the oscillator frequency jump is categorized in either fractional frequency units (33 ppb) or in equivalent velocity units, that is, the fractional frequency error times the speed of light (33 ppb×3×108 m/sec=10 m/sec).
In unaided or in tightly-coupled modes of operation, a GNSS receiver is more robust in detecting and recovering from oscillator micro jumps where the GNSS receiver is controlling the code and carrier tracking loops, than compared to an integrated Inertial Navigation System (INS)/GNSS operating in an ultra-tightly-coupled (UTC) mode of operation. In an INS/GNSS, the INS mission processor receives in phase (I) and quadrature phase (Q) data from the GNSS receiver, and controls the code and carrier tracking loops through code and carrier numerically controlled oscillator (NCO) commands. The advantages of operating in UTC mode are enhanced anti jam performance, and the ability to maintain better tracking performance during high dynamic operation. However, due to the much narrower tracking bandwidth, the UTC mode is more susceptible to quartz crystal micro-jumps.